require ('./main.css' )  
const { toLowerCase,toUpperCase } = require('./b.js')
const a = 'Hello 严总，帅的惊动党中央!!'  
console.log(toLowerCase(a)) 
console.log(toUpperCase(a))
let oDiv=document.createElement('div')
oDiv.textContent='严总真帅'
document.body.appendChild(
    oDiv
)
module.exports = a;   // common js 模块化方案  